This invention relates to an overflow-preventing valve and the application thereof. More specifically, the present invention relates to an overflow-preventing valve that effectively works for preventing a sealing oil or a lubricating oil from overflowing out of a system for a rotary machine which is used in an inorganic or organic chemical plant, a petroleum refinery plant, a plant for manufacturing chemicals and a power plant, and to the application thereof.
A conventional sealing oil supply system for a centrifugal compressor has a structure, for example, as shown in FIG. 5. In FIG. 5, a sealing oil for preventing gas from leaking out of a compressor is pressurized by a sealing oil pump 1 and is adjusted to a constant predetermined differential pressure (a difference between an oil pressure and a gas pressure) through a liquid level control valve 2 and a liquid level controller 4 to correspond to an internal pressure of a compressor 8. The sealing oil is fed to the compressor 8 through a sealing oil supply pipe 3. To control the pressure, a gas pressure transmitting pipe 6 is connected from the compressor 8 to an upper portion of a sealing oil head tank 5. Any change such as an increase or a decrease in the gas pressure in the compressor 8 is detected by the liquid level controller 4, and an air pressure signal is sent to the liquid level control valve 2 to regulate the valve in order to control a supply rate of oil, so that the predetermined differential pressure between the gas pressure in the compressor 8 and the pressure of the sealing oil is constantly maintained, thereby to prevent the gas from leaking out of a casing.
A plurality of transfer barriers 9 equipped with rubber bladders therein is provided between the sealing oil supply pipe 3 and the sealing oil head tank 5, so that the sealing oil to be fed and the oil in the sealing oil head tank 5 are kept separated from each other by the rubber bladders in the transfer barriers 9 even in the event that the pressure for supplying the sealing oil is abnormally raised due to a trouble and/or an inappropriate operation of the liquid level control valve 2 or the liquid level controller 4. Thus, the oil in the sealing oil head tank 5 is prevented from flowing into the compressor 8 through the gas pressure transmitting pipe 6. In the conventional system shown in FIG. 5, the transfer barriers 9 are usually so small that a plurality of barriers has to be provided in order to create a capacity comparable to an amount of oil in the sealing oil head tank 5.
Moreover, the sealing oil in the sealing oil head tank 5 is isolated by the sealing oil transfer barriers 9, wherein a considerable period of time is required for charging the oil to be stored in the tank beforehand, and somewhat sophisticated skill is also required for adjusting the level of the oil in the tank. Furthermore, the rubber bladders in the transfer barriers 9 are always in contact with oil and are shrunk during operation of the compressor 8 or the rubber bladders may be aged in a long usage. Thus, the bladders are hardened or broken and become defective. Therefore, in order to prevent such an accident, the transfer barriers must be regularly renewed, to cause a great burden in an maintenance cost.
Therefore, the transfer barriers 9 may be omitted to save the cost of facilities. Even though a sealing oil overflow rarely occurs, in such a case, the compressor must be disassembled and re-assembled in order to clean the overflowed sealing oil, which requires laborious work and a large amount of time. For example, in case of disassembling and re-assembling a centrifugal compressor in an ethylene producing plant, a total time was two to five days inclusive of purging with gas and re-starting (e.g. 5 men.times.12 hours.times.2 shifts.times.2 days), which also caused a production loss of several hundred million yen.
The present inventor, therefore, had studied various overflow-preventing valves but could not find any desirable valves.
For instance, (1) Japanese Patent Application Laid-Open Publication (Kokai) No. 93625/1988 discloses a device for preventing fuel from flowing out, and (2) Japanese Patent Application Laid-Open Publication (Kokai) No. 240468/1990 discloses an exhaust valve. In the case of the Publication (1), however, the device is designed to cope with a case where a fuel tank is turned sideways by about 90 degrees, so that a valve moves and comes into intimate contact with a valve seat due to the self-weight of the fuel and closes a flow path to thereby permit some fuel (oil) to flow out. Also, the valve of the Publication (1) is not quite utilizable as a stationary overflow-preventing valve that does not incline. In the case of the valve disclosed in the Publication (2) (see FIG. 3 which is a sectional view of the prior art), an orifice 21A is provided on an outlet side to separate and discharge only gas since it is not possible for the conventional discharge valve to completely prevent drain of liquid. In case a gas pressure suddenly changes in the system, however, there is another problem that the orifice 21A itself functions as a resistance, causing delay of transmission of pressure. When the above valve is used for a sealing oil supply system of FIG. 4, it is, therefore, difficult to finely adjust a liquid level.
The present inventor therefore has conducted a study, and has discovered a fact that the above-mentioned problems can be solved if a float valve 13 could be made in a shape of an inverse U-shaped cross section instead of the conventional closed spherical body 13G (see FIG. 3), and has arrived at the present invention.